In the known audio-driver technology, the conventional Class-AB driver uses fixed voltage power source, and shows poor efficiency in low-power output. The enhanced Class-G driver has a limited number of power stages, and a better efficiency than Class-AB driver; however, the Class-G driver is still unable to achieve optimal condition.
The power source for Class-H driver automatically adjusts the voltage supply according to the signal input. Although simple in concept, the design of power source to achieve rapid change based on loading is very difficult.
The conventional approach is to use the change in loading to adjust voltage supply; however, in a causality system, the demand comes before the supply. Thus, with drastic change in signal, the supply will be unstable.
U.S. Pat. No. 8,149,061 disclosed “Class H Amplifier”, wherein the disclosure adjusts the input to the control circuit by controlling the negative output node; however, an instantaneous drastic change in loading output will leave the power source insufficient time to supply a corresponding voltage.
U.S. Pat. No. 7,863,841 disclosed “Class H Drive”, wherein the approach is to use the detection of loading current to adjust the power voltage. Because the time of loading change occurs before the supply adjustment, a possible situation is that the power source may be unstable with drastic loading change.
Therefore, the issues need to be addressed include how to obtain demand message before the loading demand occurs so that an instantaneous surge in loading output will not lead to belated voltage supply, as well as free of the unstable voltage supply in case of the drastic loading change when using current loading detection as a basis for voltage adjustment.